The present invention relates to a process for preparing amines by reacting ammonia or primary or secondary amines with olefins at elevated temperatures and pressures in the presence of zeolites having an NES structure.
An overview of the methods for aminating olefins is given in xe2x80x9cFunctionalisation of Alkenes: Catalytic Amination of Monoolefinsxe2x80x9d, J. J. Brunet et al. J.Mol.Catal., 49 (1989), pages 235 to 259.
There are fundamentally two catalysis mechanisms. The olefin is coordinated to form a metal complex. This activated species can be attacked by the nucleophilic amine and form a higher aminated product. The amine can be chemisorbed on acid centers or metal centers (via metal amides) and be reacted in this activated form with the olefin.
Zeolites are very useful catalysts. They have a high number of catalytically active centers combined with a large surface area. The zeolites described differ in type and in the after-treatment (eg. thermal treatment, dealumination, acid treatment, metal ion exchange, etc.). Examples may be, found in U.S. Pat. Nos. 4,375,002, 4,536,602, EP-A-305 564, EP-A-101 921, DE-A-42 06 992.
EP-A-133 938, EP-A-431 451 and EP-A-132 736 disclose processes in which borosilicate, gallium silicate, aluminosilicate and iron silicate zeolites are used for the preparation of amines from olefins and refer to the possibility of doping these zeolites with alkali, alkaline earth and transition metals.
CA-A-2 092 964 discloses a process for preparing amines from olefins in which BETA-zeolites, which are defined as crystalline aluminosilicates having a particular composition and a pore size of more than 5 xc3x85, are used. Preference is given to using metal- or halogen-modified Beta-zeolites.
All processes for synthesizing amines from olefins over these catalysts give a low amine yield or a low space-time yield, or lead to rapid deactivation of the catalysts.
It is an object of the present invention to remedy these disadvantages.
We have found that this object is achieved by a new and improved process for preparing amines of the general formula I 
where
R1,R2,R3,R4,R5,R6 are hydrogen, C1-C20-alkyl, C2-C20-alkenyl, C2-C20-alkynyl, C3-C20-cycloalkyl, C4-C20-alkyl-cycloalkyl, C4-C20-cycloalkyl-alkyl, aryl, C7-C20-alkylaryl or C7-C20-aralkyl,
R1 and R2 are together a saturated or unsaturated divalent C3-C9-alkylene chain and
R3 or R5 are C21-C200-alkyl, C21-C200-alkenyl or together a divalent C2-C12-alkylene chain,
by reacting olefins of the general formula II 
where R3, R4, R5 and R6 are as defined above, with ammonia or primary or secondary amines of the general formula III 
where R1 and R2 are as defined above, at from 200 to 350xc2x0 C. and pressures of from 100 to 300 bar in the presence of a heterogeneous catalyst, wherein the heterogeneous catalyst used is a zeolite having an NES structure.
The process of the present invention can be carried out as follows:
The olefin II and ammonia or the primary or secondary amine III can be reacted at from 200 to 350xc2x0 C., preferably from 220 to 330xc2x0 C., particularly preferably from 230 to 320xc2x0 C., and pressures of from 100 to 300 bar, preferably from 120 to 300 bar, particularly preferably from 140 to 290 bar, in the presence of zeolites having an NES structure as catalyst, eg. in a pressure reactor, and, preferably, the amine obtained is separated off and the unreacted starting materials are recirculated.
The present invention gives a very good yield at high selectivity and at a high space-time yield. In addition, the deactivation of the catalyst has been suppressed.
In the process of the present invention, even with a low excess of ammonia or amine, a high selectivity to the desired reaction product is achieved and the dimerization and/or oligomerization of the olefin used is avoided.
One embodiment of this process comprises feeding a mixture of ammonia and/or amines III with the olefin II in a molar ratio of 1:1 to 5:1 to a fixed-bed reactor and reacting this mixture at from 200 to 350xc2x0 C. and a pressure of from 100 to 300 bar in the gas phase or in the supercritical state.
The desired product can be obtained from the mixture leaving the reactor by means of known methods, for example distillation or extraction, and can, if necessary, be brought to the desired purity by means of further separation operations. In general, the unreacted starting materials are preferably recirculated to the reactor.
It is possible to use monounsaturated or polyunsaturated olefins II, in particular those having from 2 to 10 carbon atoms or mixtures thereof, and polyolefins as starting materials. Owing to their less pronounced polymerization tendency, monoolefins are more suitable than diolefins and polyolefins, although the latter can be reacted equally selectively by means of higher excesses of ammonia or amine. The position of the equilibrium and thus the conversion to the desired amine is very strongly dependent on the reaction pressure selected. High pressure favors the addition product, although the pressure range up to 300 bar generally represents the optimum for technical and economic reasons. The selectivity of the reaction is influenced to a great extent by the temperature, as well as by parameters such as ammonia/amine excess and catalyst. Although the reaction rate of the addition reaction increases greatly with rising temperature, competing cracking and recombination reactions of the olefin are promoted at the same time. In addition, a temperature increase is not advantageous from a thermodynamic point of view. The position of the temperature optimum in respect of conversion and selectivity is dependent on the constitution of the olefin, the amine used and the catalyst and is usually in the range from 200 to 350xc2x0 C.
Suitable catalysts for the amination of olefins are zeolites having an NES structure, preferably NU-87 zeolites, which are known, for example, from EP-A-377 291.
Zeolites having an NES structure have a two-dimensional pore system with the approximate dimensions 4.7xc3x976.0 xc3x85 (Meier, Olson, Atlas of Zeolite Structure Types, 3rd Ed., 1992, Butterworth-Heinemann, pages 154 to 155). An example of a zeolite having an NES structure is NU-87 (Shannon et al., Nature 353 (1991), pp. 417 to 420). The structure of SSZ-37 (U.S. Pat. No. 5,254,514) has not yet been finally established, but it appears to be related to NU-87 (Nakagawa, Stud. Surf. Sci. Catal. 84 (1994), pages 323 to 330), so that for the purposes of this application it should also be included among the zeolites having an NES structure of the present invention.
Apart from the NES zeolites containing aluminum as trivalent element in the SiO2 matrix, as is the case, for example, in NU-87, for the purposes of this application other elements are also possible if acid centers are created by their incorporation. This is the case, for example, for borozeolites, iron zeolites or gallium zeolites. The molar ratio of SiO2 to the oxides of the trivalent elements are known as the modulus SiO2/M2O3 (M=Al, B, Ga, Fe), can vary from virtually infinity to a few tens depending on the class of zeolite.
Apart from the classical zeolites based on SiO2, it is also possible to obtain analogous structures based on aluminum phosphates, known as AlPOs. If these contain aluminum and phosphorus in a ratio of greater than 1, they are likewise acid and can be used for the purposes of the present invention. If part of the phosphorus and/or both aluminum and phosphorus is replaced by silicon, this gives the SAPOs which are likewise acid. If various metal ions such as Li, B, Be, Mg, Ti, Mn, Fe, Co, Zn, Ga, Ge, As are present in addition to aluminum and phosphorus, the compounds are referred to as MeAPOs, or in the simultaneous presence of silicon as MeAPSOs, in which the negative charge of the MeaAlbPcSidOe framework is in each case balanced by cations. All such molecular sieves having an NES structure are included among the catalysts of the present invention.
The zeolites having an NES structure of the present invention can be shaped as such or else together with a binder in a weight ratio of from 98:2 to 40:60 to give extrudates or pellets. Suitable binders are various aluminum oxides, preferably boehmite, amorphous aluminosilicates having an SiO2/Al2O3 ratio of from 25:75 to 95:5, silicon dioxide, preferably finely divided SiO2, mixtures of finely divided SiO2 and finely divided Al2O3, finely divided TiO2 and also clays. After shaping, the extrudates or compacts are advantageously dried at 110xc2x0 C. for 16 hours and calcined at from 200 to 500xc2x0 C. for from 2 to 16 hours, with the calcination also being able to be carried out directly in the amination reactor.
To increase the selectivity, the operating load and the number of possible regenerations, various modifications can be made to the zeolite catalysts having an NES structure of the present invention.
One modification of the catalysts comprises ion-exchanging or doping the unshaped or shaped zeolites with alkali metals such as Na and K, alkaline earth metals such as Ca and Mg, earth metals such as Tl, transition metals such as Ti, Zr, Mn, Fe, Mo, Cu, Zn and Cr, noble metals and/or rare earth metals such as La, Ce or Y.
In an advantageous embodiment, the shaped zeolites having an NES structure of the present invention are placed in a flow tube and, for example, a halide, an acetate, an oxalate, a citrate or a nitrate of the abovedescribed metals in dissolved form is passed over them at from 20 to 100xc2x0 C. Such an ion exchange can, for example, be carried out on the hydrogen, ammonium or alkali metal form of the zeolites having an NES structure of the present invention.
A further possible way of applying the metal to the zeolites having an NES structure of the present invention comprises impregnating the material, for example, with a halide, an acetate, an oxalate, a citrate, a nitrate or an oxide of the abovedescribed metals in aqueous or alcoholic solution.
Both ion exchange and impregnation can be followed by drying and if desired repeated calcination. In the case of metal-doped zeolites having an NES structure, an after-treatment with hydrogen and/or with steam can be useful.
A further possible way of modifying the zeolites comprises subjecting the zeolites having an NES structure of the present invention, shaped or unshaped, to a treatment with acids such as hydrochloric acid (HCl), hydrofluoric acid (HF), sulfuric acid (H2SO4), phosphoric acid (H3PO4), oxalic acid (HO2Cxe2x80x94CO2H) or mixtures thereof.
In a particular embodiment, the zeolites having an NES structure of the present invention are treated prior to shaping with one of the acids mentioned in a concentration of from 0.001 N to 2 N, preferably from 0.05 to 0.5 N, for from 1 to 100 hours under reflux. After being filtered off and washed, they are generally dried at from 100 to 160xc2x0 C. and calcined at from 200 to 600xc2x0 C. A further particular embodiment comprises an acid treatment of the zeolites having an NES structure of the present invention after they have been shaped with binders. Here, the zeolite of the present invention is generally treated for from 1 to 3 hours at from 60 to 80xc2x0 C. with a 3-25% strength acid, in particular a 12-20% strength acid, subsequently washed, dried at from 100 to 160xc2x0 C. and calcined at from 200 to 600xc2x0 C. Here too, the calcination can again be carried out directly in the amination reactor.
A further possible way of modifying the zeolites is given by an exchange with ammonium salts, eg. NH4Cl, or with monoamines, diamines or polyamines. Here, the zeolite shaped together with binder is generally exchanged continuously at from 60 to 80xc2x0 C. with 10-25% strength, preferably 20% strength, NH4Cl solution for 2 hours in a weight ratio of zeolite/ammonium chloride solution of 1:15 and then dried at from 100 to 120xc2x0 C.
A further modification which can be made to the zeolites of the present invention is dealumination in the case of aluminum zeolites, where a part of the aluminum atoms is replaced by silicon or the zeolites have their aluminum content depleted by, for example, hydrothermal treatment. A hydrothermal dealumination is advantageously followed by extraction with acids or complexing agents in order to remove non-lattice aluminum formed. The replacement of aluminum by silicon can, for example, be carried out by means of (NH4)2SiF6 or SiCl4. Examples of dealuminations of Y-zeolites may be found in Corma et al., Stud. Surf. Sci. Catal. 37 (1987), pages 495 to 503. In the case of other trivalent oxides, the modulus can be increased similarly by a part of the boron, the iron or the gallium being leeched out or replaced by silicon.
The catalysts can be used as extrudates having diameters of, for example, from 1 to 4 mm or as pellets having diameters of, for example, from 3 to 5 mm for the amination of the olefins.
A fluidizable material having a particle size of from 0.1 to 0.8 mm can be obtained from the shaped catalyst, for example in the form of extrudates, by milling and sieving.
The substituents R1, R2, R3, R4, R5 and R6 in the compounds I, II and III have the following meanings:
R1, R2, R3, R4, R5, R6 
hydrogen,
C1-C20-alkyl, preferably C1-C12-alkyl, particularly preferably C1-C8-alkyl such as methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, n-pentyl, iso-pentyl, n-hexyl, iso-hexyl, n-heptyl, iso-heptyl, n-octyl and iso-octyl,
C2-C20-alkenyl, preferably C2-C12-alkenyl, particularly preferably C2-C8-alkenyl such as vinyl and allyl,
C2-C20-alkynyl, preferably C2-C8-alkynyl, in particular C2H and propargyl,
C3-C20-cycloalkyl, preferably C3-C12-cycloalkyl, particularly preferably C5-C8-cycloalkyl such as cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl,
C4-C20-alkyl-cycloalkyl, preferably C4-C12-alkyl-cycloalkyl, particularly preferably C5-C10-alkyl-cycloalkyl,
C4-C20-cycloalkyl-alkyl, preferably C4-C12-cycloalkyl-alkyl, particularly preferably C5-C10-cycloalkyl-alkyl,
aryl such as phenyl, 1-naphthyl and 2-naphthyl, preferably phenyl,
C7-C20-alkylaryl, preferably C7-C16-alkylaryl, particularly preferably C7-C12-alkylphenyl such as 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 2-ethylphenyl, 3-ethylphenyl and 4-ethylphenyl,
C7-C20-aralkyl, preferably C7-C16-aralkyl, particularly preferably C7-C12-phenalkyl such as phenylmethyl, 1-phenylethyl and 2-phenylethyl,
R1 and R2 
together a saturated or unsaturated divalent C3-C9-alkylene chain, preferably xe2x80x94(CH2)4xe2x80x94, xe2x80x94(CH2)5xe2x80x94, xe2x80x94(CH2)7xe2x80x94 and xe2x80x94CHxe2x95x90CHxe2x80x94CHxe2x95x90CHxe2x80x94,
R3 or R5 
C21-C200-alkyl, preferably C40-C200-alkyl such as polybutyl, polyisobutyl, polypropyl, polyisopropyl and polyethyl, particularly preferably polybutyl and polyisobutyl,
C21-C200-alkenyl, preferably C40-C200-alkenyl, particularly preferably C70-C170-alkenyl,
R3 and R5 
together a divalent C2-C12-alkylene chain, preferably a divalent C3-C8-alkylene chain, particularly preferably xe2x80x94(CH2)3xe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94(CH2)5xe2x80x94, xe2x80x94(CH2)6xe2x80x94 and xe2x80x94(CH2)7xe2x80x94, in particular xe2x80x94(CH2)3xe2x80x94 and xe2x80x94(CH2)4xe2x80x94.